Camera apparatus, image server and image server system

ABSTRACT

An image server includes: a focus position control unit for determining a focus position based on a maximum value of focus evaluation detected by a picture signal level detection unit; and a focus lens driver for moving the focus lens in predetermined control volumes based on an instruction from the focus position control means; characterized in that, in case the exposure time is changed to a longer cycle than a predetermined cycle, the focus position control unit determines a large control volume corresponding to the change in exposure time and moves the focus lens with the control volume to detect the maximum value of focus evaluation and performs focus control.

This is a divisional application of application Ser. No. 10/874,328filed Jun. 24, 2004, the entire contents of which are incorporated byreference herein.

BACKGROUND OF THE INVENTION

The present invention relates to an image server which allows the userto photograph a picture as the user performs remote control of a cameravia a network such as the Internet and which transmits stable imagedata, and an image server system which connects the image server and aclient terminal via a network.

In recent years, an image server is attracting public attention whichallows the user to remotely control a camera via a network such as theInternet to obtain an image. Such an image server changes the exposuretime when the subject darkens and switches from the normal exposure modeto the long exposure mode. In case the mode is switched from the normalexposure mode to the long exposure mode, control information forautomatic control such as Auto Gain Control (hereinafter referred to asthe AGC control), Auto Iris (hereinafter referred to as the AI), AutoWhite Balance (hereinafter referred to as the AWB), and Auto Focus(hereinafter referred to as the AF) cannot properly follow the changecaused by extension of the exposure cycle. That is, in the normalexposure mode, the control information for AGC, AI, AWB and AF isobtained per frame in a predetermined cycle to perform automatic controland transmit an image data. In the long exposure mode, evaluation valueinformation is fixed for a long cycle. This leaves a strong sense ofincongruity when the normal exposure mode is switched to the longexposure mode. Moreover, such an image server cannot follow a rapidchange in brightness, for example. In such a case, the client performscontrol only after the information, resulting in poor camera operabilitywith a delay in response.

In order to prevent a time delay before a favorable output image isobtained due to a change in the incident light volume on entering thelong exposure mode, imaging apparatus has been proposed which comprisesmeans for decreasing the response speed of automatic signal volumecontrol only in the long exposure mode (see Japanese Patent Laid-OpenNo. 305671/1989).

As mentioned hereinabove, a related art image server cannot follow achange caused by an extended exposure cycle. In the long exposure mode,evaluation value information is fixed for a long cycle, and the serverhas failed to follow for example a rapid change in brightness. Moreover,when the focus is dislocated, the out-of-focus state persists, anacceptable phenomenon. While the imaging apparatus according to JapanesePatent Laid-Open No. 305671/1989 prevents iris oscillation by delayingthe response speed in order to follow the switching between exposuremodes, particular disclosure is not found concerning the Auto Focusmechanism.

Among several methods for detection a focus position in the Auto Focusmode, a method for using the high-frequency component of a picturesignal is often used by a network camera. FIG. 4 illustrates theprinciple of related art Auto Focus control. FIG. 5A shows theevaluation value level of Auto Focus and its control value of a relatedart image server in the normal exposure mode. FIG. 5B shows theevaluation value level of Auto Focus and its control value of the imageserver shown in FIG. 5A in the long exposure mode. In case a picturesignal is used to detect a focus position, the high-frequency componentof the picture signal shows its maximum value while the focus isachieved, as shown in FIG. 4. This is because a picture in focus has asteep contour, which means a rich high-frequency component is contained.From this characteristic, the focus position is at the maximum value ofthe hill of the high-frequency component or where the gradient is 0.

The related art AF control which achieves focus by using thischaracteristic is shown in FIGS. 5A and 5B. The evaluation value offocus used in this example is a high-frequency component extracted fromthe picture signal mentioned above. When the subject is out of focus,the level of the focus evaluation value is low. As the subjectsgradually becomes in focus, the level rises and reaches a maximum valuewhen the focus is achieved. Thus, in the related art, a focus lenstravels in the direction where the level of the evaluation valueincreases and a position where the maximum value is obtained isdetermined as a focus position.

In pursuit of a focus position, the focus lens travels in equaldistances in accordance with the control value. The term “equaldistances” is used for simplicity and the real control procedure will begiven later. For the long exposure time, an instruction for movement isissued per 1V (timing period of vertical synchronizing signal). Thefocus lens travels in equal distances in the direction where the levelof the focus evaluation value rises. As shown in FIG. 5A, the focusevaluation value rises with a change in control value (travel of thefocus lens) and reaches a maximum value at a point. Then the evaluationvalue level drops at time point T7. This shows that the focus evaluationvalue has dropped after it has peaked. This trend indicates that thecontrol value (travel position of focus lens) immediately preceding thepoint where the focus evaluation value has dropped can be employed as afocus control value. Thus the focus lens is set to this value.

In the long exposure mode, the cycle where a picture signal is obtainedis extended with the extension of the exposure period, and accordinglythe signal level detection cycle is extended, and the cycle where thefocus lens position is set is extended as a matter of fact. All thisphenomena result in a slower response. While FIG. 5B shows a doubleexposure time where the exposure time is double the normal exposuretime, the response time until focusing exceeds double that in normalexposure as the period until the focus evaluation value reaches amaximum value (time until t7*) exceeds double that in the normalexposure. In the related art image server and image server system,position setting of the focus lens is extended while in the longexposure mode. This takes time in focus control, with poor responsivity.

While the focus lens travels in equal distances in the foregoingexample, focus evaluation values of various magnitudes are obtained sothat the travel volume is controlled with relation to the gradient inorder to accommodate this phenomenon. A gradient is detected at thestart of control. When the gradient is larger than a predeterminedvalue, the dislocation of focus is assumed to be large so that controlis made using a large travel volume. In case the gradient is smallerthan the predetermined value, the current position is near a peak sothat control is made using a small travel volume, The former indicates ahill-climbing phase to approach a peak while the latter is a phase forchecking the peak position. The travel volume is changed in accordancewith the gradient in a phase also.

Assuming that the motor for driving a focus lens is a stepping motorsthe focus lens travels while being rotated in 16 steps, 12 steps or 8steps in accordance with the gradient in a hill-climbing phase withsteep gradient. In a peak-checking phase with mild gradient, the focuslens travels while being rotated in 4 steps, 2 steps or 1 step inaccordance with the gradient. Focusing takes time when in the longexposure mode even in case the travel volume is changed between phases.Thus the responsivity remains poor.

Further, as mentioned above, an image server according to the relatedart transmits to a client an image of a subject which gives a visualsense of incongruity due to a sudden increase in the brightness of thesubject during switchover between exposure modes. In this way, the imageserver and the image server system according to the related art has noother choice than transmit am image which gives a visual sense ofincongruity for example when the system has entered the long exposuremode.

SUMMARY OF THE INVENTION

The invention has as an object to provide an image server which assuresfocusing operation with no delays and maintains high controllabilitydespite a change in exposure time and which is capable of transmitting astable high-quality image.

Additionally, the invention has as an object to provide an image serverand an image server system capable of transmitting a stable high-qualityimage rather than an image which gives a visual sense of incongruitywhen the exposure time has changed.

In order to solve the problems, according to first aspect of theinvention, an image server comprises focus position controller fordetermining a focus position based on a maximum value of focusevaluation detected by picture signal level detector; and a focus lensdriver for moving the focus lens in predetermined control volumes basedon an instruction from the focus position controller; characterized inthat, in case the exposure time is changed to a longer cycle than apredetermined cycle, the focus position controller determines a largecontrol volume corresponding to the change in exposure time and movesthe focus lens with the control volume to detect the maximum value offocus evaluation and performs focus control.

In case the exposure time is changed and a long exposure mode isactivated where a picture signal is output in a longer cycle than apredetermined cycle, the focus position controller determines thecontrol volume for moving the focus lens depending on the exposure modewhich is preferably equal to the control volume in the normal exposuremultiplied by the long exposure period/normal exposure period, andthereby promptly detects the maximum value of focus evaluation todetermine the focus position based on the maximum value. This ensurespleasant Auto Focus control while requiring a short time in focusingeven in the long exposure mode. Moreover, it is possible to maintainhigh controllability and transmit a stable high-quality image.

According to second aspect of the invention, it is provided a cameraapparatus comprising signal level detector for detecting the signallevel of a picture signal output from imaging device; and picture signallevel controller for adjusting the level of a picture signal output fromthe imaging device; the camera apparatus performing picture signalprocessing on and compressing a picture signal output from the picturesignal level controller to output image data; characterized in thatcontrol level adjuster is provided for determining the correction volumeused by the picture signal level controller in level adjustment of apicture signal and that, in case the exposure time of the imaging deviceis changed to output a picture signal in a longer cycle than apredetermined cycle, the control level adjuster determines thecorrection volume in accordance with the exposure time and the signallevel detected by the signal level detector and the picture signal levelcontroller performs level adjustment of a picture signal by using thecorrection value.

In case an exposure time is changed and a long exposure mode isactivated where a picture signal is output in a longer cycle than apredetermined cycle, it is possible to correct a control value of thepicture signal level controller used by the level adjustment means forlevel adjustment by using a correction value corresponding to theexposure time. This provides control while extending a response time foronly a short period and performs adjustment of a signal level in thelong exposure mode in nearly the same response time as that in thenormal exposure mode. Thus, even when the exposure time has changed,image data is transmitted with no delays. Moreover, it is possible tomaintain high controllability and transmit a stable high-quality imageeven in case a rapid change has taken place in brightness.

Further, according to third aspect of the invention, it is provided animage server connected to a network, the image server outputting shotimage data to the network, comprising: picture signal level controllerfor automatically adjusting the signal level of a picture signal outputfrom imaging device; signal level detector for detecting the signallevel of the image signal level-adjusted by the picture signal levelcontroller; image data transmitter Lor capturing and compressing thepicture signal whose signal level is adjusted by the picture signallevel controller, converting the picture signal to a predetermined imagedata format, and transmitting the resulting signal to the network;exposure controller for controlling the exposure time of the imagingdevice; and transient state controller for controlling the image datatransmitter when the exposure time is changed by the exposurecontroller.

When the exposure time has changed, the image data indicating the signallevel of the transient state is transmission-adjusted by the transientstate controller. This transmits a stable high-quality image rather thanan image which gives a visual sense of incongruity even when theexposure time has rapidly changed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an image server and an image server systemaccording to Embodiment 1 of the invention;

FIG. 2 is a block diagram of the image server according to Embodiment 1of the invention;

FIG. 3 illustrates the evaluation levels and its control values in AutoFocus control of the image server according to Embodiment 1 of theinvention in the long exposure mode;

FIG. 4 illustrates the principle of related art Auto Focus control;

FIG. 5A shows a change in Auto Focus evaluation value level and itscontrol value of the image server according to the related art in thenormal exposure mode;

FIG. 5B shows the evaluation value level of Auto Focus and its controlvalue of the image server shown in FIG. 5A in the long exposure mode;

FIG. 6 illustrates the output signal level and its correction volume ofthe image server according to Embodiment 2 of the invention in the longexposure mode;

FIG. 7 illustrates the signal component levels and its control values inthe white balance control of the image server according to Embodiment 3of the invention;

FIG. 8 is a block diagram of the image server according to Embodiment 4of the invention;

FIG. 9 shows the output signal level and its control value of the imageserver in the normal exposure mode;

FIG. 10 illustrates the output signal level and its data transmission ofthe image server according to Embodiment 5 of the invention in the longexposure mode;

FIG. 11 is a flowchart of the exposure control operation of the cameraaccording to Embodiment 5 of the invention;

FIG. 12 is a flowchart of control operation of compression/transmissionbased on the signal level determination by the image server according toEmbodiment 5 of the invention;

FIG. 13 is a flowchart of compression/transmission by using the counterof the image server according to Embodiment 5 of the invention;

FIG. 14 illustrates the output signal level and its data transmission ofthe image server according to Embodiment 6 of the invention in the longexposure mode;

FIG. 15 is a flowchart of the exposure control operation of the cameraaccording to Embodiment 6 of the invention;

FIG. 16 is a flowchart of control operation of compression/transmissionbased on the signal level determination by the image server according toEmbodiment 6 of the invention;

FIG. 17 is a flowchart of compression/transmission by using the counterof the image server according to Embodiment 7 of the invention;

FIG. 18 illustrates the output signal level and its data transmission ofthe image server according to Embodiment 8 of the invention in the longexposure mode; and

FIG. 19 illustrates the output signal level and its data transmission ofthe image server according to Embodiment 5 of the invention in the longexposure mode.

FIG. 20 shows the exposure time control in the long exposure mode by wayof the AGC value.

FIG. 21 shows the exposure time control in the long exposure mode by wayof the image signal level.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

An image server and an image server system according to Embodiment 1 ofthe invention are described referring to drawings. FIG. 1 is a blockdiagram of an image server and an image server system according toEmbodiment 1 of the invention. FIG. 2 is a block diagram of the imageserver according to Embodiment 1 of the invention.

In FIG. 1, a numeral 1 represents an image server which photographs asubject and transfers image data, 2 a client terminal such as a PC whichis employed by the user to receive and display the image transferredfrom the image server 1 and which is capable of controlling the imageserver 1 by way of a camera control signal, and 3 a network such as theInternet which is capable of transferring an image and transmitting acamera control signal. A numeral 4 represents a DNS server whichconverts a domain name used for access to an IP address. The imageserver system according to Embodiment 1 comprises an image server 1, aclient terminal 2 and a network 3. The client terminal will be describedlater.

Referring to FIG. 2, a numeral 5 represents a camera provided in theimage server 1 for picking up an image of a subject and converting thesubject image to an image signal and output the resulting image signal.A numeral 51 represents imaging device comprising imaging elements suchas a CCD or CMOS for performing photoelectric conversion of a subjectimage, and 52 light quantity adjustment means which controls thequantity of light input to the imaging device 51 and which may comprisethe shutter feature of the imaging device 51 although mechanicaldiaphragm is often used.

A numeral 53 represents picture signal level controller which controlsthe level of a picture signal output from the imaging device 51 andwhich performs AGC control to optimize the signal level by increasingthe gain when the signal level output from the imaging device 51 isdecreased. The picture signal level controller 53 is designed to cause apicture signal to follow a target gain value or light quantity value byadjusting the picture signal with an adjustment gain value which willnot give a visual sense of incongruity. In case the image of a subjecthas suddenly turned bright, the image will return to predeterminedbrightness after a certain period has elapsed. Detection of the signallevel of a picture signal is made by calculating the average value ofpicture signal level for one frame output from the imaging device 5 a.Based on the detection result, gain control by the picture signal levelcontroller 53 is made. AGC control is implemented by the signal leveldetector 5 d and the picture signal level controller 53.

The numeral 54 picture signal processor which processes the outputsignal from the picture signal level controller 53 and generates aluminance signal (Y) and chrominance signals (Cb, Cr), 541 signal leveldetector which extracts the high-frequency component of the outputsignal (luminance signal) of the picture signal processor by way of ahkgh-pass filter or an bandpass filter and detects the high-frequencycomponent as a focus evaluation value.

Specific processing made by the picture signal processor 54 includesluminance/chrominance separation, CDS (correlated double sampling),white balance, contour correction and gamma correction. The generatedpicture signal may be in the form in which the luminance signal andchrominance signal are separate from each other, a form in which thesesignals are synthesized, or a form of primary colors R, G, B. While thecamera 5 is built into the image server 1 in Embodiment 1, the camera 5may be an external camera separate from the image server 1. A numeral 55represents a focus lens which can travel to the focus position for AFcontrol.

Detection of the signal level of a picture signal may be made bycalculating the average value of picture signal level for one frameoutput from the imaging device 51. Based on the detection result, gaincontrol by the picture signal level controller 53 is made. AGC controlis implemented by the signal level detector 54 and the picture signallevel controller 53.

A numeral 6 represents image signal compressor which captures aluminance signal and a chrominance signal input from the camera 5 with apredetermined timing and which compresses/encodes the image signal. Theimage signal compressor 6 includes an image capture control means forcontrolling the image capturing. Compression by the image signalcompressor 6 is made in a format such as JPEG and MPEG, followed by DCT(Discrete Cosine Transform) processing, quantization and encoding and apredetermined header is added. The DCT processing performs discretecosine transform on an image signal in order to represent it in the DOCTcoefficient as a frequency component. Each DOCT coefficient is dividedby each coefficient as an element of a quantization table to quantizethe coefficient. Encoding converts the quantization coefficientcalculated by this quantization to data volume tailored to the framerate of the network.

A numeral 7 represents an imaging device driver which generates a drivesignal for the imaging device 51, 71 a focus lens driver which comprisesa motor for moving the focus lens 55. The focus lens driver 51 moves thefocus lens in units of a predetermined travel volume up to the focusposition. A numeral S represents a controller which performs control ofthe picture signal processor 54, control of the focus lens driver 71(AF), control of the light quantity adjustment means 52 (AI) and AGC/AWBcontrol. The controller 8 performs control to change the imagecompression mode as well as generate HTML data and image data inaccordance with an instruction transmitted from a browser running on theclient terminal 2 via the network 3. By way of a drive mode instructedby the controller 8 the drive signal for the imaging device 51 and thefocus lens driver 71 are operated to change the focus.

A numeral 81 represents control level adjuster which performs AGCcontrol when the exposure time is change and the long exposure mode isactivated. The A&C control performed by the control level adjuster isbasically the same as the operation for normal auto gain control. Notethat, in the long exposure mode, separate control from the normalexposure mode is partially made on the correction volume of the setvalue for the picture signal level controller 53 in accordance with thepicture signal level. In case the exposure time is 2V (double the timingperiod of vertical synchronizing signal), the correction volume of theset value for the picture signal level controller 53 is double the basiccorrection volume in the normal exposure mode. Thus, the responsivity ofAGC control in the long exposure mode is equivalent to that in thenormal exposure mode.

A numeral 82 represents focus position controller which records perexposure time as an evaluation value the high-frequency component of aluminance signal detected by the signal level detector 541 in AF controland which calculates the evaluation value change ratio mentioned laterto determine that the evaluation value has become a maximum value. Thefocus position controller 82 issues a travel instruction per change inexposure time to the focus lens driver 71 to cause the focus lens driver71 to move the focus lens 55 in predetermined travel volumes and setsthe position where Locus is achieved as a focus position. The evaluationvalue per exposure time is stored into the evaluation value storagesection 101 of the storage section mentioned later.

A numeral 83 represents control level adjuster for performing AGCcontrol when the exposure time is changed and the lona exposure mode isactivated. AGC control by the control level adjuster 83 is basically asthat under (1) through (5) described below although calculation of acorrection volume for the picture signal level controller 53 ispartially different from that in the normal exposure mode as mentionedlater.

Specific operation of AGC control is described below. First, (1) thesignal level detector 54 calculates the average value of the level of apicture signal concerning the brightness for one frame output from theimaging device 51. The “picture signal output from the imaging device 5”refers to a signal level-adjusted by the picture signal level controller53. Next, (2) the signal level detector 54 communicates the averagevalue of the detected picture signal level to the camera controller 8.Next, (3) the controller 8 compares the picture signal levelcommunicated from the signal level detector 54 with a preset referencelevel and calculates the difference between the two. Next, (4) thecontroller 8 uses a preset reference table or function for AGC controlto calculate the correction volume for the picture signal levelcontroller 53. Next, (5) the control means 8 communicates the calculatedcorrection volume to the picture signal level controller 53. Then, (6)the picture signal level controller 53 changes the gain of the amplifier(that is, adds the gain correction volume to the preset gain of theamplifier to re-set the gain of the amplifier) based on the gaincorrection volume communicated from the camera controller 8, therebyadjusting the picture signal output from the imaging device 51. This isthe end of AGC control procedure. In order to detect a picture signallevel per frame and perform AGC control, acquisition and adjustment ofpicture signal level is performed in a period equivalent to the cyclewhere a picture signal is output.

The reference level refers to the level of a target picture signal to beautomatically adjusted by way of AGC control, and is for example thelevel of a picture signal where the average value of a picture signalfor one frame is equal to the brightness of 50%. The reference level isset to a visually appropriate value but may be changed by way ofoperation outside the network.

A numeral 84 represents transient state controller for determining thatthe image signal level has settled in a predetermined reference rangebased on the image signal level detected by the signal level detector541 and performing the initial image processing after the change inexposure time to restart compression and transmission of image data whenthe exposure time is changed and the long exposure mode is activated. Anumeral 85 represents picture signal level controller for controllingthe light quantity adjustment means 52 and the picture signal leveladjustment means 53 based on the picture signal level obtained from thepicture signal processing circuit and the change in exposure mode.

A numeral 9 represents a network interface connecting the server 1 andthe network 3. The network interface 3 transmits an instruction from thebrowser to the camera 5 as well as transmits HTML data and image datafrom the image server 1 to the network 3. A numeral 10 represents astorage section used by a CPU of the controller 8 to read a program ordata. A numeral 101 represents an evaluation value storage section whichstores the evaluation value per exposure time in order to detect themaximum value of evaluation in AF control. The evaluation value storagesection 101 also stores the calculated evaluation value change ratioeach time the focus lens driver 71 moves the focus lens.

The image server 1 in Embodiment 1 executes AF control when the normalexposure mode is switched to the long exposure mode. A change in AutoFocus evaluation value on mode change and its control value aredescribed below FIG. 3 illustrates the evaluation levels and its controlvalues in Auto Focus control of the image server according to Embodiment1 of the invention in the long exposure mode. FIG. 5A shows a change inAuto Focus evaluation value level and its control value applicable toalso the image server according to Embodiment 1 in the normal exposuremode, which is referenced herein.

As shown in FIG. 5A, the focus position controller 8 b moves the focuslens in accordance with the control value in order to detect a focusposition in the normal exposure mode in AF control. A travel instructionis issued per TV period of the normal exposure time (timing duration ofvertical synchronizing signal) and the focus lens travels in equaldistances in the direction where the level of the focus evaluation valuerises. This is to execute hill-climbing servo as shown in FIG. 4. Thefocus position controller 8 b detects a focus evaluation value for eachtravel and calculates a ratio of the detected focus evaluation value tothe evaluation value last detected. The ratio is the evaluation valuechange ratio which shows a change in the gradient of an evaluationvalue. By way of example, in FIG. 5A, the change volume is A and Brespectively for a period from time point T1 to time point T2 and aperiod from time point T2 to time point T3, so that the evaluation valuechange ratio is B/A. Similarly, the evaluation value change ratio is C/Bfor a period from time point T2 to time point T3 and a period from timepoint T3 to time point T4, and D/C for a period from time point T4 totime point T5 and a period from time point T5 to time point T6, and F/D,E/F, etc. A change in gradient is the difference between times. Thetravel volume is fixed so that the evaluation change ratio shows achange in gradient. The focus position controller 8 b calculates theevaluation value change ratio and stores it into the evaluation valuestorage section 10 a.

In this way, the focus evaluation value increases with the elapse oftime, that is, a change in evaluation value (travel of focus lens) andis peaked at time point T6, then decreases again at time point T7. Thisis determined that the evaluation value level and the evaluation valuechange ratio have switched from positive to negative. The focusevaluation value reaches a maximum value at time point T6 and thendecreases again. It is thus understood that the control valueimmediately preceding the time point where the focus evaluation valuedecreases is the focus control value. The focus position controller 8 bsets this value as the focus position of the focus lens.

In the long exposure mode, in the 2V period (double the (timing durationof vertical synchronizing signal) from time point T1 to time point T2,double exposure of normal exposure mode is provided so that the lengthof a cycle where a focus evaluation value is obtained is doubled, asshown in FIG. 3. The length of a cycle where the focus lens travels isalso doubled. Thus the focus lens is made to travel with the controlvolume double that in the normal exposure mode. To be more precise, acontrol volume obtained by multiplying the control volume in the normalexposure mode by [long exposure period/normal exposure period] ispreferable. The resulting travel volume per 1V is the same. Similar tothe normal exposure mode, the change volume A between the evaluationvalue level at time point T1 and that at time point T2 is stored. Next,in the 2V period from time point T2 to time point T3, the focus lens ismade to travel with the same control volume for the period from timepoint T1 to time point T2. The change volume B between the evaluationvalue level at time point T2 and that at time point T3 is obtained. Thechange volume B is compared with the change volume A and the ratio ofthe change volume B to the change volume A, that is, the evaluationvalue change ratio B/A is calculated.

The above calculation is continued. In case the evaluation value changeratio B/A has dropped below a predetermined value such as 0.05, it isunderstood that the evaluation value level is neat a maximum value. Thefocus position controller 8 b preferably reduces the control volume atthe next time point. For example, the focus position controller 8 bshould return to the control volume for 1V in the normal exposure.Detailed calculation is continued in this state, same as the control innormal exposure. The evaluation value decreases from time point T4 totime point T5 as shown in FIG. 3. The focus position controller 8S thendetermines the control value at time point T4 as the focus position. Atthe same time, the focus position commoller 8 b sets the focus positionof the focus lens with the 1V period. This control reduces time tofocusing even in the double exposure. In case the evaluation valuechange ratio B/A is not below the predetermined value such as 0.05 andthe evaluation value change ratio B/A is reversed to negative, themaximum value of the evaluation value level is detected at time pointT2. In this case, a focus position is located near the focus lensposition at time point T2 so that control is made to return the focuslens position to approach that at time point T2 to determine the focuslens position where the evaluation value level is at its maximum. Inthis procedure also, the focus position controller 8 b makes controlwhile performing detailed calculation, same as in the normal exposuremode, so as to determine as a focus position the control value at timepoint T4 b where the evaluation value decreases.

In this way, the image server and the image server system according toEmbodiment 1 can perform pleasant Auto Focus control with quick focusingeven in the long exposure mode. It is possible to perform AF control forequivalent time period and maintain high controllability as well astransmit a stable high-quality image. In particular, the image server iseffective as an image server comprising a camera which calculates theevaluation value of Auto Focus control per frame.

According to the embodiment as mentioned above, in case the exposuretime is changed and a long exposure mode is activated where a picturesignal is output in a longer cycle than a predetermined cycle, the focusposition controller determines the control volume for moving the focuslens depending on the exposure mode which is preferably equal to thecontrol volume in the normal exposure multiplied by the long exposureperiod/normal exposure period, and thereby promptly detects the maximumvalue of focus evaluation to determine the focus position based on themaximum value. This ensures pleasant Auto Focus control while requiringa short time in focusing even in the long exposure mode. Moreover, it ispossible to maintain high controllability and transmit a stablehigh-quality image.

Calculation for determining the focus position is made easy.

It is possible to detect a precise position when the maximum value isdetected.

The ratio of change in focus evaluation value is minutely measured sothat it is possible to detect a precise position when the maximum valueis detected.

It is readily possible to detect a focus position from the picturesignal obtained from the imaging device.

Image data is transmitted with no delays despite a change in exposuretime. It is possible to obtain a stable high-quality image even in casea rapid change has taken place in brightness.

Second Embodiment

The image server 1 according to Embodiment executes level adjustmentcontrol when the system is switched from the normal exposure mode tolong exposure mode. The signal level and its correction volume in modechange are described below. Same signs as those of the image server ofEmbodiment 1 shown in FIGS. 1 and 2 show the same components so that thedetails will be omitted.

FIG. 6 illustrates the output signal level and its correction volume ofthe image server in the long exposure mode according to Embodiment 2 ofthe invention. FIG. 9 shows the output signal level and its controlvalue of the image server according to the invention in the normalexposure mode.

FIG. 9 is an explanatory drawing which shows the level of a signaloutput in a normal exposure mode of a related image server and itscontrol value. In FIG. 9, the signal level of 1V period exposure isdetected at the time point Ta. Note that 1V is the timing of a verticalsynchronizing signal. The difference K between a signal level and areference level and an exposure time are used to obtain the correctionvolume A for AGC, AE and AWB in exposure. In accordance with a change inthe correction volume A, the control value for each control is changed.After the next V period, correction values B, C, D are obtained andsequentially specified in accordance with the differences L, M, Lbetween signal levels and the reference level, and the signal level isfinally changed into a reference level. The correction volumes A, B, C,Dare determined so that the brightness will change gradually by way ofAGC control in consideration of a response speed and a change in thebrightness of an image on the screen, in order to follow a rapid changein brightness and secure stability.

In the long exposure time of Embodiment 2, the signal level of 2V-periodexposure is detected with the signal level detector 541 at a time pointTb as shown in FIG. 6. Note that 1V is a timing of a verticalsynchronizing signal. The signal level detector 541 communicates thedetection result to the controller 8. The controller 8 determines thatthe exposure mode is the long exposure mode and starts AGC control byway of the control level adjuster 83. The control level adjuster 83compares the picture signal level communicated from the signal leveldetector 54 with a preset reference level and calculates the differencebetween the two. Next, the control level adjuster 83 calculates a gaincorrection volume A* by using a preset AGC reference table or functionfrom the difference K and the exposure time 2V. Operation of calculationof the correction volume A*, using the reference table is describedbelow referring to Table 1.

TABLE 1 Level difference X Basic correction volume Y 1 1 5 1 10 3 30 560 8 100 14 150 20 200 30 300 50

Table 1 which shows the basic correction volume for the level differenceX is stored in the storage means 10. While not shown, a value in thereference table assumed in case the level difference X is a negativevalue is one preceded by a minus sign (−) in a value in Table 1. Forexample, in case the calculated level difference X is 200, the basiccorrection volume is 30. The exposure time is 2V (double exposure unittime) so that the calculated correction volume is twofold. Thecorrection volume is obtained using the expression: A*=(basic correctionvolume Y corresponding to the level difference X×(unit time countP)=30×2=60.

Next, the method for calculating a gain correction volume by using afunction is described below. A correction volume obtained by arithmeticoperation is calculated based on an arithmetic expression whosevariables are the difference X between the signal level and thereference level and the exposure time.

As an arithmetic expression, the arithmetic expression:Gain correction volume=X×Log(X ²)×P×a, where P*=√{square root over ( )}Pand a=0.05.In case each variable is X=100, P=2 (unit exposure time), the correctionvolume=100×4×1.4×0.05=28. Table 2 shows the arithmetic operation resultobtained in case P=2.

TABLE 2 Correction volume Level difference X X × Log(X²) × {square rootover (P)} × 0.05 1 0 5 0.49 10 1.41 30 6.24 60 15.04 100 28.2 150 46.02200 64.88 300 84.52

By using such an arithmetic expression, the need for using a referencetable is eliminated so that it is no longer necessary to reserve astorage area for a reference table. Thus, in case an arithmeticexpression can be used, the arithmetic expression can be used to obtaina correction volume.

The arithmetic expression in Table 2 above has X and P as variables. Itis of course possible to provide an arithmetic expression using X as avariable per value of P, that is, exposure time. By doing so, thestructure of the arithmetic expression is made simpler by using P as anadditional variable, which facilitates use of an arithmetic expression.

By also considering the change ratio W of a picture signal output fromthe imaging device 51, it is possible to higher-precision picture signallevel control. For example, the difference between the level of apicture signal output from the imaging device 52 in the 2V period of Tathrough Tb (hereinafter referred to as the “ab” period) and thereference level is X, which is used to obtain the correction volume A*.The difference between the picture signal level in the 2V period of Tbthrough Tc (hereinafter referred to as the “bc” period) obtained fromthe control value corrected with the correction value A* and thereference level is L. Thu, the change ratio is represented in theexpression: W=(L−L)/A*. In case the difference between the product ofthe correction volume B* obtained from the difference L between thepicture signal level and the reference level at the time point Tc and W(expected signal level change volume) between L, that is L−B*×W is anegative value, correcting a control value by using the correctionvolume B* is expected to result in the picture signal level smaller thanthe reference level, so that the correction volume B* obtained isreplaced with B*X×W. In case B*×W is a positive value, the correctionvolume B* is used.

In this way, by adding the change ratio W of the picture signal outputfrom the imaging device 51, it is possible to perform more precisepicture signal level control.

The correction volume A* thus calculated is communicated from thecontrol level adjuster 83 to the picture signal level controller 53,which changes the amplifier gain of the picture signal level controller53 based on the correction volume communicated from the controller 8 andadjust the picture signal output from the imaging device 51. What isnecessary is to be able to obtain a proper correction volumecorresponding to the exposure time. For example, the basic gaincorrection volume corresponding to level X may be multiplied by 1.7 forthe double exposure time or 2.2 for the triple exposure time, withoutsimply being multiplied by the number of exposure time units.

The correction volumes B:, C:, D* per 2V exposure time (Tc, Td, Te) arecalculated with the same calculation method. In case the leveldifference X is between values in Table 1, X is complimented by anotherlevel difference in the reference table. For example, in case the leveldifference X is 20, the basic correctionvolume=3+(5-3)×(20-10)/(30-10)=4.

While the reference table (Table 1) includes some of the reveldifferences X and other level differences are complimented to obtaincorrection volumes, the reference table may be created to cover alllevel differences. For calculation of correction values in casesufficient memory is available.

As mentioned above, the AGC control count per unit time is smaller inthe long exposure mode than in the normal exposure mode. The picturesignal level controller 53 adjusts the signal level of a picture signalwith the correction volume corresponding to the exposure time so thatthe response time is not extended P-fold (unit exposure time count) withrespect to the normal exposure time but the correction volume changes inaccordance with the ratio of exposure time X long exposure time. Thisensures signal level adjustment in an equivalent time (equal time or alittle longer time) to that in the normal exposure time. This allows thepicture signal level controller 5 a to change the gain and follow thesignal level in the same procedure as in the normal exposure mode.

When the normal exposure mode is switched to the long exposure mode, thepicture signal level detected by the signal level detector 5 d rapidlychanges. The signal level is made stable near the reference value by wayof AGC control. Thus, in calculation of a correction volume after thesignal level has settled near the reference value or after apredetermined time has elapsed, calculation procedure may be donesimilarly to the normal exposure mode without multiplying the exposureP.

For the same exposure time, a value corresponding to the leveldifference X may be preset and the basic correction volume Y may bemultiplied by the value. This value is preset in a reference table orcalculated by using an arithmetic expression whose variables are X andP.

For the exposure time 2V, a level difference X smaller than or equal to10 may be set to a multiplication value of 1, a level difference Xlarger than 10 to smaller or equal to 30 a multiplication value of 1.5,and a level difference X larger than 30 a multiplication value of 2. Inthis case, when X=10, a correction volume of 3 is obtained from themultiplication value of 1 corresponding to Y=3 and the exposure time.When X=30, a correction volume of 7.5 is obtained from themultiplication value of 1.5 corresponding to Y=3 and the exposure time.When X=200, a correction volume of 60 is obtained from themultiplication value of 2 corresponding to Y=30 and the exposure time.By doing so, it is possible, when the exposure time is prolonged, to setthe AGC response time close to that in the normal exposure mode as wellas perform proper AGC control which is tailored to the taste of a personbrowsing an image from the image server. In particular, in case theexposure time is considerably long, such as 10-fold, this procedure canprevent possible overshooting of the reference level caused by simplemultiplication of X by P.

While the basic correction volume Y is multiplied by the ratio P offunctions of exposure time to obtain the correction volume in exposurein this example, an arithmetic expression whose variables are Y and Pmay be used instead.

In this way, the image server and the image server system do not show aresponse time P times as long as that in the normal exposure mode evenwhen the normal exposure mode is switched to the long exposure mode. Thecorrection volume changes in accordance with the ratio of exposure timeP×long exposure time, thereby allowing signal level adjustment in anequivalent time (equal time or a little longer time) to that in thenormal exposure time. This allows the picture signal level controller 53to change the gain and follow the signal level in the same procedure asin the normal exposure mode. When the signal level is below thepredetermined range, adjustment is possible in accordance with thechange ratio for adjustment in the normal exposure mode, which preventsovershooting of the reference level. While the picture signal levelcontroller 53 is used to adjust the picture signal level in thisexample, light quantity adjustment means 54 may be used instead of thepicture signal level controller 53.

Embodiment 3

An image server according to Embodiment 3 of the invention concernswhite balance control. FIG. 7 illustrates the signal component levelsand its control values in the white balance control of the image serveraccording to Embodiment 3 of the invention.

The basic operation of the white balance control is described below.When the imaging device 51 outputs an R signal component, G signalcomponent and B signal component, the picture signal processor 54amplifies or attenuates the R signal component and the B signalcomponent to control the components to the same level as the G signalcomponent. In case a complementary signal is output from the imagingdevice 51, the R signal component, C signal component and B signalcomponent are generated by way of arithmetic operation and the R signalcomponent and B signal component are amplified or attenuated to controlthe components to the same level as the G signal component. Note that,in some cases, the R signal component and B signal component arecontrolled so that each of them will maintain a predetermined leveldifference from the G signal component. For example, the signalcomponent level is the R signal component level or B signal componentlevel and the reference level is a value having a predetermined leveldifference from the G signal component level. To be more precise,depending on an image, both R signal component and B signal component isgiven a desired weight with respect to the G signal component in orderto set a level target value. The target value may change from moment tomoment with a change concerning the subject or a change in colortemperature.

The while balance control at switchover from normal exposure mode tolong exposure mode in Embodiment 3 is substantially the same as that inEmbodiment 2 except that the signal level is replaced with the signalcomponent level processed by the picture signal processor 54. Thus, thedetails are omitted and the operation will be outlined below.

Referring to FIG. 8, at a time point Tb, the signal level detector 5 d 1detects the signal component level under exposure of 2V period. Thesignal level detector 541 in Embodiment 3 performs level detection of Rsignal component and B signal component. The signal level detector 541communicates the detection result to the camera controller 8. From thedifference K between the signal component level and the reference leveland the exposure time, the control level adjuster 8 a in Embodiment 4obtains the correction volume A* in exposure. The correction volume iscalculated in the same procedure as that in Embodiment 2. Note that thecorrection volume to be calculated is used to correct the picture signallevel concerning color, not picture signal level concerning brightness.

The correction volume A* thus calculated is communicated from thecontrol level adjuster 8 a to the picture signal level controller 53,which changes the chrominance signal component level adjustment value ofthe picture signal level controller 53 to adjust the picture signaloutput from the imaging device 5 a based on the correction volumecommunicated from the camera controller 8.

The correction volumes B*, C: D per 2V exposure time (Tc, Td, Te) arecalculated by using the same calculation method.

In this way, the image server and the image server system according toEmbodiment 3 do not show a response time P times as long as that in thenormal exposure mode even when the normal exposure mode is switched tothe long exposure mode. The control correction volume changes inaccordance with exposure time, thereby allowing signal level adjustmentin the same time as that in the normal exposure time. This allows thepicture signal processor 53 to change the gain and follow the signallevel in the same procedure as in the normal exposure mode and controlthe white balance.

Embodiment 4

Embodiment 4 of the invention is an image server of Embodiment 1 exceptthat a built-in server is omitted. FIG. 8 shows the block diagram of animage server according to Embodiment 4 of the invention. Same signs asthose of the image server of Embodiment 1 shown in FIGS. 1 and 2 showthe same components so that the details will be omitted.

Referring to FIG. 8, a numeral 80 represents a camera controller forcontrolling a camera 5 separate from the image server which photographsa subject and outputs an image signal. The camera controller 80 drivesthe imaging device 5 a of the camera 5, controls the picture signalprocessor 5 d, controls the light quantity adjustment means 52 (AE) andperforms AGC/AWB control at specific levels.

The controller 8 performs control to change the image compression modeand generate HTML data and image data in accordance with an instructionby the browser running on the client terminal 2 transmitted from thenetwork 3 via the network interface 9. In order to perform signal leveladjustment in the same way as the adjustment made for a predeterminedcycle, and in order to compress an image signal and transmit image datain the same cycle as the image signal, the controller 8 and the controllevel adjuster 83 instruct the camera controller 80 to control theimaging device 51, picture signal processor 54, light quantityadjustment means 52, and perform AGC/AWB control.

In this way the image server does not have a built-in camera 5 and mayhave an external camera. Thus various image servers may be providedthrough combination with the camera 5, which assures convenience.

While the image server has been described in Embodiments, the inventionis not limited thereto but any other imaging apparatus performing AGCcontrol and AWB control may be employed instead.

In case an exposure time is changed and a long exposure mode isactivated where a picture signal is output in a longer cycle than apredetermined cycle, it is possible to correct a control value of thepicture signal level controller used by the level adjustment means forlevel adjustment by using a correction value corresponding to theexposure time. This provides control while extending a response time foronly a short period and performs adjustment of a signal level in thelong exposure mode in nearly the same response time as that in thenormal exposure mode. Thus, even when the exposure time has changed,image data is transmitted with no delays. Moreover, it is possible tomaintain high controllability and transmit a stable high-quality imageeven in case a rapid change has taken place in brightness.

According to the embodiments as mentioned above, it is possible toperform appropriate level adjustment in accordance with the exposuretime even after the normal exposure mode is switched to the longexposure mode.

The level adjustment means uses a preset reference table or function sothat calculation of a correction value based on the exposure time andsignal level is made easy. The control value of the picture signal levelcontroller is adjusted by using the level correction value so that it ispossible to perform proper AGC control and AWB control in accordancewith the exposure time. This performs adjustment of a signal level inthe long exposure mode in a short period.

The correction value is calculated based on the exposure time, picturesignal level and ratio of change in picture signal level, which allowshigh-precision level adjustment.

As the signal level approaches the reference level. The correction valuedecreases, which prevents excessive control. The user does not feel asense of incongruity about the image.

It is thus possible to perform proper AGC control in accordance with theexposure time.

It is thus possible to perform proper AWB control in accordance with theexposure time.

It is thus possible to provide an image server system capable ofperforming proper picture signal adjustment in accordance with theexposure time.

It is thus possible to provide an image server system capable ofperforming proper picture signal adjustment in accordance with theexposure time.

Embodiment 5

Control of image data transmission is described below which takes placewhen the image server 1 of the Embodiment is switched from the normalexposure mode to the long exposure mode.

FIG. 10 illustrates the signal level output from the image serveraccording to the invention in the long exposure mode and thecorresponding data transmission.

T1 through T14 shown in part (a) are vertical synchronizing timings as areference for operation of an image server. As an alternative, a timinggenerated by separately provided timing signal generation means may beused for control. Part (b) shows the exposure start timing and T1through T4 correspond to the normal exposure mode. The exposure starttiming basically matches the picture signal read timing fro the imagingdevice 51. At T5, readout of a picture signal (Image Read) from theimaging device 51 is halted and the long exposure mode having theexposure time double that of the normal exposure mode is selected (inthe following procedure, readout of a picture signal is made with everyother timing of the vertical synchronizing signal, etc.) In this case,the picture signal from the imaging device 5 a is read with the timingT6, as shown in part (c).

In part (e), at time points T1 through T4, the picture signal in thenormal exposure mode is captured by the image capture control means 61and compressed and transmitted with the timings of T2 through T5 asshown in part (f). The signal level of the picture signal captured in aperiod T6 through T7 is based on the long exposure mode. The exposuretime is longer than in the normal exposure mode, so that the signallevel detected by the signal level detector 541 is high as shown at T7in part (g). The picture signal level adjustment means 53 performs leveladjustment so as to decrease the gain of the signal level of the picturesignal captured after T8, based on the signal level detected by thesignal level detector 541. With the timing T1, the picture signal levelin the long exposure settles at a predetermined level.

In the period from time points T5 through T11, the picture signal levelis high as shown in part (g). Compressing the picture signal withoutlevel adjustment and transmitting the compressed signal will result inoutput of a picture signal of an irregular level caused by a rapidincrease in the picture signal level, which gives a sense f incongruity.This is why the picture quality is degraded on the related art imageserver in switchover between exposure modes.

In Embodiment, once switchover has taken place between exposure modes,while the picture signal level is detected by the signal level detector541 and it is determined that the signal level is out of the referencerange by the transient state controller 84, compression/transmission ofthe picture signal is halted. The transient state controller 84 may beprovided with timing signal generation means and the timing signal maybe generated or halted in order to control compression/transmission of apicture signal. Thereafter, based on an instruction from the picturesignal level controller 85, the picture signal level adjustment means 53performs AGC control. When the transient state controller 84 determinesthat the signal level is within the reference range,compression/transmission of a picture signal is restarted.

Control operation of the image server according to the Embodiment isdescribed below.

FIG. 11 is a flowchart of the exposure control operation of the cameraaccording to Embodiment 5 of the invention. FIG. 12 is a flowchart ofcontrol operation of compression/transmission based on the signal leveldetermination by the image server according to Embodiment 5 of theinvention. FIG. 13 is a flowchart of compression/transmission by usingthe counter of the image server according to Embodiment 5 of theinvention.

Exposure control operation of the camera 5 is described below referringto FIG. 14. The controller 8 checks whether a request for change ofexposure time has been issued to the image server in the standby statefrom the network (step 1). In case the request has been issued, thecontroller 8 sets the change of exposure time (step 2) to adjust theexposure time. The camera 5 acquires the signal level LTold of the finalimage before the change of exposure time (step 3) and outputs it to thecontroller 8 then execution returns to step 1. In case a change requesthas not been issued in step 1, the camera 5 acquires the signal levelLTnew of the latest image (step 4) and outputs it to the controller 8then execution returns to step 1.

Control operation of compression/transmission based on the picturesignal level determination by the image server is described belowreferring to FIG. 12. After a request for a change of exposure time ismade and the change of the exposure time is set, it is checked whetheran image output from the picture signal processor 54 is the first imageafter the change of exposure time (step 11). In case the image output isthe first image after the change of exposure time, the signal levelLTnew is acquired by the signal level detector 541 (step 12) and outputto the controller 8. Then the image capture control means 84 startscapture operation (step 13). Next the transient state controller 84calculates (LTnew-LTold)/LTold from the signal levels LTnew and LTold,and checks whether the calculated value falls within the reference range(step 14). In case the value is within the reference range, assumingthat variations in the signal level at switchover between exposure modeshave terminated, the transient state controller 84 completes the statusof the first image processing after the change of exposure time (step15), compresses the image data in the image data transmitter 6, andtransmits the image data via the network interface 9 (step 16). In casethe calculated value is not within the reference range in step 14,execution returns to step 11. In case the image output from the picturesignal processor 54 is not the first image after the change of exposuretime in step 15, assuming that switchover between exposure modes isover, the transient state controller 84 completes the status of thefirst image processing after the change of exposure time.

Described below is the control operation of compression/transmission bycounting the number of images after change of exposure time using acounter instead of compression/transmission based on the determinationof the image signal level. As shown in FIG. 13, after a request for achange in exposure time is issued and setting of the exposure time ischanged, it is checked whether the image output from the picture signalprocessor 54 is the first image after the change of exposure time (step21). The counter is set to 0 as an initial value. In case the image isthe first one after the change of exposure time in step 21, thetransient state controller 84 checks whether the counter has reached apredetermined reference value (step 22). In case the counter has not yetreached the reference value, the transient state controller 84increments the counter by 1 (step 23) then control returns to step 21.In case the counter has reached the predetermined reference value instep 22, assuming that variations in the signal level at switchoverbetween exposure modes have terminated, the transient state controller84 completes the status of the first image processing after the changeof exposure time (step 24), compresses the image data in the image datatransmitter 6, and transmits the image data via the network interface 9(step 25). In case the image output from the picture signal processor 54is not the first image after the change of exposure time in step 21,execution proceeds to step 25. Assuming that switchover between exposuremodes is over, the transient state controller 84 completes the status ofthe transient image processing after the change of exposure time.

In this way, the image server and the image server system according toEmbodiment 5 can halt compression of image data and transmission ofcompressed data until the image signal level settles at a level withinthe predetermined reference range after the change of exposure time soas not to output several images with large variations in brightness whenthe normal exposure mode is switched to the long exposure mode. Thistransmits only a stable high-quality image at switchover betweenexposure modes.

Embodiment 6

An image server according to Embodiment 6 of the inventionenables/disables the capture control means 6 to halt transmission of animage. In case capture of an image is not performed, compression ortransmission of an image is not carried out. FIG. 14 illustrates thesignal level output from the image server in the long exposure mode andits data transmission in Embodiment 6 of the invention. Configuration ofthe image server according to Embodiment 6 is basically the same as thatin Embodiment 5 and same signs show the same components. Thus Embodiment6 refers to FIGS. 1 and 2 also.

T1 through T4 shown in FIG. 14 are vertical synchronizing timings as areference for operation of an image server. Part (b) shows the exposurestart timing and T1 through T4 correspond to the normal exposure mode.As shown in part (e1), capture operation is enabled. The High level ofthe signal corresponds to the enable mode. At T5 in part (e1), readoutof a picture signal (Image Read) from the imaging device 51 is haltedand the long exposure mode having the exposure time double that of thenormal exposure mode is selected. Capture operation is also disabled. Asshown in part (c), the picture signal from the imaging device 5 a isread with the timing T6.

A picture signal in the normal exposure mode at each of T1 through T4 iscaptured by the image capture control means 61 andcompressed/transmitted with the timings T2 through T5 as shown in part(f). The signal level of the image signal captured at T6 is based on thelong exposure mode. The exposure time is longer than in the normalexposure mode, so that the signal level detected by the signal leveldetector 541 is high as shown at T7 in part (g). The picture signallevel adjustment means 53 performs level adjustment so as to decreasethe gain of the signal level of the picture signal captured after T8,based on the signal level detected by the signal level detector 541.With the timing T11, the picture signal level in the long exposuresettles at a predetermined level. When the signal level falls within thereference range, capture operation is enabled. Capture operation isrestarted in synchronization with the picture signal output from thepicture signal processor 54. Compression/Transmission of the imagesignal is restarted.

In the period from time points T5 through T11, the picture signal levelis high as shown in FIG. 10. Compressing the picture signal withoutlevel adjustment and transmitting the compressed signal will result inoutput of a picture signal of an irregular level caused by a rapidincrease in the picture signal level, which gives a sense f incongruity.This is why the picture quality is degraded on the related art imageserver in switchover between exposure modes.

In case the camera 5 and the image data transmitter 6 are provided inseparate blocks, it is possible to enable/disable the capture operationof the image capture control means 61 by way of a capture control signalwith control made easy. The change volume of signal level when theexposure time is changed can be estimated so that the period up to thetime point where the signal level settles in the reference range can beestimated to some degree. Instead of monitoring that the signal levelfalls within the reference range, the time period starting with thechange of exposure time may be monitored and image transmission startedwhen a predetermined time has elapsed.

Control operation of the image server according to Embodiment 6 isdescribed below. FIG. 15 is a flowchart of the exposure controloperation of the camera according to Embodiment 6 of the invention. FIG.16 is a flowchart of control operation of compression/transmission basedon the signal level determination by the image server according toEmbodiment 6 of the invention. FIG. 17 is a flowchart ofcompression/transmission by using the counter of the image serveraccording to Embodiment 6 of the invention.

Exposure control operation of the camera 5 is described below referringto FIG. 15. The controller 8 checks whether a request for change ofexposure time has been issued to the image server in the standby statefrom the network (step 31). In case the request has been issued, thecontroller 8 sets the change of exposure time (step 32) to adjust theexposure time. The controller 8 acquires the signal level LTold of thefinal image before the change of exposure time (step 33). The transientstate controller 84 drives LOW the capture enable for the image capturecontrol means 61 (step 34) and execution returns to step 31.

In case a change request has not been issued in step 31, the camera 5acquires the signal level LTnew of the latest image (step 35). Thetransient state controller 84 calculates (LTnew−LTold)/LTold from thesignal levels LTnew and LTold, and checks whether the calculated valuefalls within the reference range (step 36). In case the value is withinthe reference range, assuming that variations in the signal level atswitchover between exposure modes have terminated, the transient statecontroller 84 drives the capture enable HIGH (step 37) and waits in step31 again. In case the value is out of the reference range, the transientstate controller 84 also waits in step 31 again.

Control operation of compression/transmission by way of a capturecontrol signal of the image server is described below referring to FIG.16. After a request for a change in exposure time is issued and thechange of exposure time is set, the capture enable state is acquired(step 41). This process is repeated until the acquired capture enablestate is driven HIGH (step 42), then the image capture control means 84starts capture operation (step 43). Then the image data is compressed inthe transmission means 6 and transmitted from the network interface 9(step 44).

Described below is the exposure control operation by counting the numberof images after change of exposure time using a counter (not shown)instead of exposure control operation based on the determination of thesignal level in steps 31 through 37. As shown in FIG. 17, the controller8 checks whether a request for change of exposure time has been issuedto the image server in the standby state from the network (step S5), Incase the request has been issued, the controller 8 sets the change ofexposure time (step 52) to adjust the exposure time. The controller 8acquires the signal-level LTold of the final image before the change ofexposure time (step 53). The transient state controller 84 drives LOWthe capture enable for the image capture control means 6 a (step 54) andsets the counter to 0 as an initial value (step 55). It is checkedwhether the counter value is equal to or more than the reference value(step 56). In case the counter value is smaller than the referencevalue, the counter value is incremented by 1 (step 57), then executionreturns to step 51. In case the counter value is equal to or more thanthe reference value, the capture enable is driven HIGH (step 58) andexecution returns to step 51 again where the image server waits in thestandby state.

In this way, according to Embodiment 6, once switchover has taken placebetween exposure modes, while the signal level is detected by the signallevel detector 541 and it is determined that the signal level is out ofthe reference range by the transient state controller 84, the imagecapture control means 61 is disabled to halt capture operation therebyhalting compression/transmission of an image signal. Thereafter, in caseit is determined that the signal level has fallen within the referencerange, several images with large variations in brightness are outputfrom the imaging device 51 when the normal exposure mode is switched tothe long exposure mode in order to restart compression and transmissionof the image signal.

Note that the images are not transmitted to the user of the image serveruntil the image signal level has settled at a level in the predeterminedreference level.

Embodiment 7

An image server according to Embodiment 7 of the inventionenables/disables the image capture operation to halt transmission of animage, same as the image server in Embodiment 5. The picture signallevel adjustment means 5 c is forcibly changed in a rapid fashion whenthe exposure time is changed, in order to improve the responsively to achange in signal level.

FIG. 18 illustrates the signal level output from the image server in thelong exposure mode and its data transmission in Embodiment 7 of theinvention, Configuration of the image server according to Embodiment 7is basically the same as that in Embodiment 6 and same signs show thesame components. Thus Embodiment 7 refers to FIGS. 1 and 2 also.

T1 through T4 are based on the normal exposure mode and captureoperation is enabled as shown in part (e1) in FIG. 15. The High level ofthe signal corresponds to the enable mode. At T5 in part (e1), readoutof a picture signal (Image Read) from the imaging device 51 is haltedand the long exposure mode having the exposure time double that of thenormal exposure mode is selected. Capture operation is also disabled. Asshown in part (c), the picture signal from the imaging device 51 is readwith the timing T6.

The signal level of the image signal captured at T6 is based on the longexposure mode. The exposure time is longer than in the normal exposuremode, so that the signal level detected by the signal level detector 541is high as shown at T7 in part (g) A change in signal level is estimatedbefore T6. In accordance with an instruction from the picture signallevel controller 85, the picture signal level adjustment means 53decreases the signal level by the estimated change in signal level. Thisestimation is made based on the change ratio of exposure time. Forexample, when the normal exposure mode is switched to the long exposuremode having the exposure time double that of the normal exposure mode,the brightness is expected to be about twofold, so that a gain is set toreduce the signal level to half. When the signal level falls within thereference range, the capture operation is enabled and image signalcapture is restarted in synchronization with the picture signal output.Compression/Transmission of an image signal is restarted at the sametime.

In the period from time points T5 through T11, the signal level is highas shown in part (g). Transmitting the signal without level adjustmentwill result in a rapid increase in the image signal level, which gives asense f incongruity. According to the image server in Embodiment 7, thepicture signal level adjustment means 51 forcibly decreases the signallevel and the image capture control means 61 is disabled, thus it ispossible to halt compression/transmission of an image signal.

In case the camera 5 and the image data transmitter 6 are provided inseparate blocks, it is possible to enable/disable the capture operationof the image capture control means 61 by way of a capture control signalwith control made easy. The change volume of signal level when theexposure time is changed can be estimated so that the period up to thetime point where the signal level settles in the reference range can beestimated to some degree. Instead of monitoring that the signal levelfalls within the reference range, the time period starting with thechange of exposure time may be monitored and image transmission startedwhen a predetermined time has elapsed.

It is possible to previously suppress a change in signal level byforcibly changing the signal level, so that it is possible to output animage of a stable level to a network despite transient level instabilityby improving the response to a change in signal level caused by a changein exposure time.

While capture operation is enabled/disabled in Embodiment 7, a systemmay be employed where all image signals are captured but transmission ofan image signal to the network is controlled depending on the detectedpicture signal level, same as Embodiment 5.

Embodiment 8

Embodiment 8 of the invention is an image server of Embodiment 5 exceptthat a built-in server is omitted. FIG. 19 illustrates the signal leveloutput from the image server in the long exposure mode and its datatransmission in Embodiment 3 of the invention. Components having thesame signs as those of the image server in Embodiment 5 shown in FIGS. 1and 2 show the same component, so that the detailed description isomitted.

Referring to FIG. 19, a numeral 80 represents a camera controller forcontrolling a camera 5 separate from the image server which photographsa subject and outputs an image signal. The camera controller 80 drivesthe imaging device 51 of the camera 5, controls the picture signalprocessor 54, controls the light quantity adjustment means 52 (AE) andperforms ACC/AWB control at specific levels.

The controller 8 performs control to change the image compression modeand generate HTML data and image data in accordance with an instructionby the browser running on the client terminal 2 transmitted from thenetwork 3 via the network interface 9. In order to compress an imagesignal and transmit image data in the same cycle as the image signal,the controller 8 instructs the camera controller 80 to control theimaging device 51, picture signal processor 54, light quantityadjustment means 52, and perform ACC/AWB control.

In this way the image server of Embodiment does not have a built-incamera 5 and may have an external camera. Thus various image servers maybe provided through combination with the camera 5, which assuresconvenience.

While the picture signal level is controlled as AGC control by thepicture signal level adjustment means 53 when the exposure time ischanged in Embodiments 5 through 8, the light quantity adjustment means52 may be used to change the quantity of light input to the imagingdevice 51 thereby controlling the picture signal level.

While the change in exposure time is described as a change in exposuretime concerning a longer exposure time than the normal exposure time inEmbodiments 5 through 8, the same control may be made on a change inexposure time concerning a shorter exposure time than the normalexposure time, such as a change in exposure using a shutter feature ofthe imaging device 51.

According to the above-mentioned embodiments, when the exposure time haschanged, the image data indicating the signal level of the transientstate is transmission-adjusted by the transient state controller. Thistransmits a stable high-quality image rather than an image which gives avisual sense of incongruity even when the exposure time has rapidlychanged.

It is thus possible to transmit a stable high-quality image rather thanan image which gives a visual sense of incongruity even when theexposure time has rapidly changed.

Transmission control is made in accordance with the output of the timermeans despite a rapid change in exposure time, thereby transmitting astable high-quality image.

Transmission control is made in accordance with the counted output ofthe counter means despite a rapid change in exposure time, therebytransmitting a stable high-quality image.

Capture operation is halted by the transient state controller despite arapid change in exposure time, thereby transmitting a stablehigh-quality image.

Compression is halted by the transient state controller despite a rapidchange in exposure time, thereby transmitting a stable high-qualityimage.

It is possible to previously suppress a change in signal level, so thatit is possible to output an image of a stable level to a network despitetransient level instability by improving the response to a change insignal level caused by a change in exposure time.

Image capture control is readily performed by way of a timing signalgenerated by the timing signal generation means.

The image data indicating the signal level in the transient state is notcaptured by the transient state controller. It is thus possible totransmit a stable high-quality picture rather than an image which givesa visual sense of incongruity.

It is thus possible to transmit a stable high-quality image rather thanan image which gives a visual sense of incongruity even when theexposure time has rapidly changed.

Operation of switchover from the normal exposure mode to the longexposure mode may be performed by the client through manual observationof an image. For example, when an exposure mode selector button isspecified from the input means of the client, the selection informationis transmitted to the image server.

Based on the selection information transmitted from the client, theimage server switches to the mode different from the current exposuremode (from the normal exposure mode to the long exposure mode; or fromthe long exposure mode to the normal exposure mode).

The exposure mode selector button is transmitted as screen displayinformation from the image server. The client displays the exposure modeselector button on the display based on the information.

As mentioned above, operation of switchover from the normal exposuremode to the long exposure mode may be performed by the client throughmanual observation of an image. The following describes a method forautomatically switching from the normal exposure mode to the longexposure mode and a method for automatically switching from the longexposure mode to the normal exposure mode:

First, a switching method by way of AGC on the image signal processingmeans 5 d is described below referring to FIG. 20.

FIG. 20 shows the exposure time control in the long exposure mode by wayof the AGC value. When the illumination of a subject drops, increase ofgain starts. When the illumination of the subject further has droppedand the AGC control value has reached A, the exposure time is increased(the exposure time parameter is incremented by 1), and the AGC value isdecremented by C with respect to the image signal in the new exposuretime. In case the illumination of the subject has further dropped, theexposure time is increased again (the exposure time parameter isincremented by 1), and the AGC value is decremented by C with respect tothe image signal. The decrement C of the AGC value is made equivalent tothe volume of increase in the image level due to long exposure so as toreduce the variation in the image level actually output. When thelongest exposure time is set (MAX EXT setting in the above figure), theAGC gain is increased to a maximum value of (B) even in case the AGCvalue reaches A.

Conversely, when the illumination of the subject has risen and the AGCvalue has become A−(C+F), the exposure time is decreased (The exposuretime parameter is decremented by 1), and the AGC value is incremented byC with respect to the image signal. In case the illumination of thesubject has further risen, the exposure time is decreased again (theexposure time parameter is decremented by 1), and the AGC value isincremented by C with respect to the image signal.

In case the illumination of the subject has risen in the normal exposuremode (1/60s), state transition is made to Iris control, same as thenormal exposure mode.

An exposure time of 01 or above corresponds to long exposure in theabove example. That is, the AGC level is used to determine a drop in theillumination of the subject and state transition is made to the longexposure mode. By assuming the AGC level A in the above figure as AGCMAX value B, it is possible to lower the illumination level whereswitchover to long exposure takes place and suppress the reduction offrame rate due to low illumination. The series of control is made by thecontroller 8.

Next, a switching method by way of the detection level of the signallevel detector 5 d 1 is described below referring to FIG. 21.

FIG. 21 shows the exposure time control in the long exposure mode by wayof the image signal level.

Controls such as AGC work even in low illumination to retain the imagesignal at a constant level (A). When the illumination has furtherdropped and AGC has reached MAX, the image signal level starts to drop.When the image signal level has reached a predetermined value B, thelong exposure (01) is selected. Then the image level rises. As theillumination further drops, the image level drops to Level B, where theexposure time is switched to 02. This causes the image signal to riseagain. When the illumination has further dropped and the image signallevel B is reached, the maximum exposure time: MAX EXT is selected. Inthe maximum exposure time, the image signal level continues to drop asthe illumination further drops.

Conversely, when the illumination of the subject has risen and the imagesignal level rises to reach Level C in the long exposure mode, a shorterexposure time is selected. For example, in the case of r exposure time:MAX EXT in the above figure, the exposure time 02 is selected. Switchingto the shorter exposure time 02 causes the image signal level to droptemporarily. When the illumination of the subject further rises, theexposure time is switched: 02 to 01 to 00 (normal exposure).

In this way, by switching between exposure times by using the imagesignal level, it is possible to automatically switch from the normalexposure mode to the long exposure mode or switch from the long exposuremode to the normal exposure mode. The series of control is made by thecontroller 8 based on the information from the signal level detector 5 d1 of the image signal processing means 5 d.

In the embodiments of this invention, the imaging means is implementedby a CCD or a CMOS image sensor. Available products are MN39143FT(Matsushita Electric Industrial Co., LTD.), ICX228AK (Sony Corporation),and MN39321PD (Matsushita Electric Industrial Co., LTD.).

The image signal level means is implemented by an AFE (Analog FrontEnd). Available products are CXA2006Q (Sony Corporation), AD9898 (AnalogDevices, Inc.), HD49334 (Hitachi, Ltd.), and IR3Y50M (SHARPCORPORATION).

As image signal processing means, HD49815 (Hitachi, Ltd.), CXD261CBR(Sony Corporation), and LR38603A (SHARP CORPORATION) are available.

The image signal compressor is implemented by a JPEG compressor.Available products are MD2208 (FUJIFILM Microdevices Co., Ltd.) andLC82210 (SANYO Electric Co., Ltd.).

The control means is implemented by a microcomputer. Available productsare HD64F2238 (Hitachi, Ltd.), HD6417709 (Hitachi, Ltd.), andMN103E010HRA (Matsushita Electric Industrial Co., LTD.).

The storage section is implemented by a memory, Available products areMT48LC4M16A2 (Micron Technology, Inc.), MT48LCSM16A2 (Micron Technology,Inc.), MSM51V18165D (Oki Electric Industry Co., Ltd.), and HY5DV641622(Hynix Semiconductor Inc.).

The network interface is implemented by a LAN controller. Availableproducts are RTL8019AS (Realtek Semiconductor Corp.) LAN91C113I (SMSC),and LAN91C96 (SMSC).

As mentioned above, according to the camera apparatus, an image serverand an image server system of the invention, it is readily possible tocalculate the correction volume based on the exposure time and signallevel. The control value of the picture signal level controller isadjusted using this level correction volume thus allowing proper AGCcontrol and AWB control in accordance with the exposure time andproviding signal level adjustment in the long exposure mode in a shortperiod. It is thus possible to maintain high controllability despite achange in exposure time and transmit a stable high-quality image even incase a rapid change has taken place in brightness. A reference table ora function is used for processing, which makes easy the calculation ofthe correction volume. It is thus possible to provide an image serversystem capable of performing proper picture signal level adjustment inaccordance with the exposure time.

Further, it is possible to transmit a stable high-quality image withoutoutputting an image of an irregular level when the exposure time hasbeen changed.

CROSS REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority ofJapanese Patent Application Nos. 2003-182326 and 2003-182327 both filedon Jun. 26, 2003 and No. 2003-325838 filed on Sep. 18, 2003, thecontents of which are incorporated herein by reference in its entirety.

1. A camera apparatus comprising: an imaging unit that converts incidentlight into a picture signal with an exposure time selected from among atleast a first exposure time and a second exposure time, the secondexposure time being longer than the first exposure time, and the picturesignal having a signal level; and an adjusting unit that adjusts thesignal level in accordance with the signal level, wherein if saidimaging unit converts the incident light into the picture signal withthe second exposure time, said adjusting unit adjusts the signal levelin accordance with both the signal level and the second exposure time,wherein said adjusting unit determines a correction volume in accordancewith the signal level and adjusts the signal level in accordance withthe correction volume, and wherein if said imaging unit converts theincident light into the picture signal with the second exposure time,said adjusting unit determines the correction volume in accordance withboth the signal level and the second exposure time.
 2. The cameraapparatus according to claim 1, wherein said adjusting unit adjusts thesignal level in accordance with the correction volume for white balancecontrol.
 3. The camera apparatus according to claim 1, wherein saidadjusting unit determines the correction volume in accordance with thesignal level using at least one of a preset reference table and afunction.
 4. The camera apparatus according to claim 3, wherein at leastone of the preset reference table and the function is based on a changeratio of the signal level.
 5. The camera apparatus according to claim 1,wherein the signal level represents brightness of the incident light. 6.A camera apparatus comprising: an imaging unit that converts incidentlight into a picture signal with an exposure time selected from among atleast a first exposure time and a second exposure time, the secondexposure time being longer than the first exposure time, and the picturesignal having a signal level; and an adjusting unit that adjusts thesignal level in accordance with the signal level, wherein if saidimaging unit converts the incident light into the picture signal withthe second exposure time, said adjusting unit adjusts the signal levelin accordance with both the signal level and the second exposure time,wherein said adjusting unit compares the signal level with apredetermined level and adjusts the signal level in accordance with thecomparison result, and wherein if said imaging unit converts theincident light into the picture signal with the second exposure time,said adjusting unit adjusts the signal level in accordance with both thecomparison result and the second exposure time wherein said adjustingunit determines a correction volume in accordance with the comparisonresult and adjusts the signal level in accordance with the correctionvolume, and wherein if said imaging unit converts the incident lightinto the picture signal with the second exposure time, said adjustingunit determines the correction volume in accordance with both thecomparison result and the second exposure time.
 7. The camera apparatusaccording to claim 6, wherein said adjusting unit determines thecorrection volume in a manner that the correction volume decrease as thedifference between the signal level and the predetermined leveldecreases.
 8. The camera apparatus according to claim 6, wherein thesignal level represents a brightness of the incident light.
 9. A cameraapparatus comprising: an imaging unit that converts incident light intoa picture signal with an exposure time selected from among at least afirst exposure time and a second exposure time, the second exposure timebeing longer than the first exposure time, and the picture signal havinga signal level; and an adjusting unit that adjusts the signal level inaccordance with the signal level, wherein if said imaging unit convertsthe incident light into the picture signal with the second exposuretime, said adjusting unit adjusts the signal level in accordance withboth the signal level and the second exposure time, wherein said imagingunit outputs the picture signal with a predetermined cycle, and whereinif said imaging unit converts the incident light into the picture signalwith the second exposure time, said adjusting unit adjusts the signallevel in accordance with the predetermined cycle.
 10. The cameraapparatus according to claim 9, wherein said adjusting unit adjusts thesignal level with a cycle equivalent to the predetermined cycle.
 11. Thecamera apparatus according to claim 9, wherein the signal levelrepresents a brightness of the incident light.
 12. A camera apparatuscomprising: an imaging unit that converts first incident light into afirst picture signal having a first signal level and second incidentlight into a second picture signal having a second signal level, thefirst picture signal and the second picture signal being periodicallyconverted by the imaging unit in accordance with an exposure timeselected from among at least a first exposure time and a second exposuretime, the second exposure time being larger than the first exposuretime, and the first picture signal being converted by the imaging unitbefore the second picture signal; and an adjusting unit that adjusts thesecond signal level in accordance with a correction volume that isdetermined in accordance with the first signal level and the secondexposure time.
 13. The camera apparatus according to claim 12, whereinthe correction volume is larger when the first picture signal isassociated with the second exposure time than when the first picturesignal is associated with the first exposure time.
 14. The cameraapparatus according to claim 12, wherein the correction volume is largeras a function of increased length of the second exposure time.
 15. Thecamera apparatus according to claim 12, wherein the adjusting unitdetermines the correction volume in accordance with a preset referencelevel and the first signal level, and the correction volume is larger asa function of increased difference between the preset reference leveland the first signal level.
 16. The camera apparatus according to claim12, wherein the first and second signal levels represent brightness ofincident light.
 17. The camera apparatus according to claim 12, whereinthe first and second signal levels represent an average value relatingto brightness for one frame converted by the imaging unit.
 18. Thecamera apparatus according to claim 12, wherein the adjusting unitadjusts the second signal level by changing a gain of an amplifier. 19.The camera apparatus according to claim 12, further comprising acommunication unit that communicates with a communication apparatus,wherein the communication unit transmits to the communication unit thesecond picture signal having the second signal level adjusted by theadjusting unit.
 20. An image server transmitting a picture signal tonetwork, the image server comprising: an imaging unit that convertsfirst incident light into a first picture signal having a first signallevel and second incident light into a second picture signal having asecond signal level, the first picture signal and the second picturesignal being periodically converted by the imaging unit in accordancewith an exposure time selected from among at least a first exposure timeand a second exposure time, the second exposure time being larger thanthe first exposure time, the first picture signal being converted by theimaging unit before the second picture signal; an adjusting unit thatadjusts the second signal level in accordance with a correction volumethat is determined in accordance with the first signal level and thesecond exposure time, and a transmitter that transmits, to the network,the second picture signal having the adjusted second signal level. 21.An image processing method comprising: converting first incident lightinto a first picture signal having a first signal level and secondincident light into a second picture signal having a second signallevel, by periodically converting the first picture signal and thesecond picture signal in accordance with an exposure time selected fromamong at least a first exposure time and a second exposure time, thesecond exposure time being larger than the first exposure time, and thefirst picture signal being converted before the second picture signal;and adjusting the second signal level in accordance with a correctionvolume that is determined in accordance with the first signal level andthe second exposure time.